In connectors as connecting components for electronic devices for consumer use and for vehicle use, materials are used in which base plating of Ni or Cu is applied to the surface of brass or phosphor bronze materials and Sn or Sn alloy plating is further applied to the base plating. Sn or Sn alloy plating is generally required to have properties such as low contact resistance and high solder wettability, and further, recently the reduction of the insertion force has also been required at the time of joining together a male terminal and a female terminal molded by press processing of plating materials. In the production process, on the plating surface, there occur sometimes whiskers, which are needle crystals, causing problems such as short circuiting, and hence such whiskers are also required to be suppressed satisfactorily.
In this regard, Patent Literature 1 discloses an electrical contact material including a contact base material, a ground layer composed of Ni or Co, or an alloy of both of Co and Ni and formed on the surface of the contact base material, and an Ag—Sn alloy layer formed on the surface of the ground layer, wherein the average concentration of Sn in the Ag—Sn alloy layer is less than 10 mass %, and the concentration of Sn in the Ag—Sn alloy layer is varied with a concentration gradient so as to increase from the interface with the ground layer toward the surface layer portion of the Ag—Sn alloy layer. According to Patent Literature 1, an electrical contact material excellent in wear resistance, corrosion resistance and processability is described, and the electrical contact material is described to be able to be produced with an extremely low cost.
Patent Literature 2 discloses a material for electric/electronic components wherein on the surface of a substrate having a surface composed of Cu or a Cu alloy, through the intermediary of an intermediate layer composed of a Ni layer or a Ni alloy layer, a surface layer composed of a Sn layer or a Sn alloy layer is formed, each of these layers containing an Ag3Sn (ε phase) compound and having a thickness of 0.5 to 20 μm. As described in Patent Literature 2, an object of the invention described in Patent Literature 2 is to provide a material for electrical/electronic components, wherein the surface layer is lower in melting point than Sn, excellent in solderability, and free from the occurrence of whisker; the joint strength of the junction formed after soldering is high and at the same time the temporal degradation of the joint strength at high temperatures is hardly caused, and hence the material is suitable for a lead material; even when the material is used in a high-temperature environment, the increase of the contact resistance is suppressed, the material does not cause the degradation of the connection reliability with the counterpart member, and hence the material is suitable as a contact material, the object also including the provision of a method for producing the above-described material, and the provision of electrical/electronic components using the above-described material.
Patent Literature 3 discloses a covering material including a base material having electrically conductive property and a covering layer formed on the base material, wherein the covering layer includes an intermetallic compound of Sn and a precious metal at least on the surface side thereof. Patent Literature 3 describes an object thereof is to provide a covering material being low in contact resistance, having a low friction coefficient so as to be effective in reduction of insertion force, being excellent in oxidation resistance and having stable properties over a long period of time, and a method for producing the covering material.